In the development of semiconductor devices, particularly, semiconductor storage devices, miniaturization of memory cells has been advanced to achieve a large capacity, a low cost, and the like. For example, the development of a three-dimensional NAND type flash memory device in which memory cells are three-dimensionally disposed has been advanced. In the three-dimensional NAND type flash memory device, a NAND string in which memory cells are connected in a direction (so-called vertical direction) perpendicular to surfaces of word line layers is formed in the word line layers stacked with a dielectric layer therebetween. As a result, high integration is achieved as compared with a case where the memory cells are two-dimensionally disposed. To achieve higher integration, it has been proposed to divide a memory film physically by vertical division using lithography technology to form a plurality of memory films extending in the vertical direction to thereby form memory cells, for example, twice as many as existing memory cells. However, if the formed memory film is physically divided using the lithography technology, a memory film structure may be damaged.